1. Field of the Invention
This invention relates generally to nucleic acid sequences encoding proteins that are associated with abiotic stress responses and abiotic stress tolerance in plants. In particular, this invention relates to nucleic acid sequences encoding proteins that confer drought, cold, and/or salt tolerance to plants.
2. Background Art
Environmental stress causes significant crop losses. The stresses are numerous and often crop- or location-specific. They include drought, high salinity, temperature extremes, hypoxia, mineral nutrient deficiency and UV-B radiation. Research in this area is driven by the hope of improving crop yield in afflicted areas. Currently, actual, but slow advances are being made by crop breeders and agronomists using tried- and tested-methodology. However, biotechnology will increasingly have a role as genes involved in stress tolerance are cloned and their mode of action elucidated (Quarrie S A, 1996 Plant Growth Reg. 20:167–178). By improving a plant's performance in response to different environmental stresses, the losses in productivity and risks to farming can be greatly reduced. Modifying a plant's tolerance to environmental stresses also allows a plant to be grown in regions where a plant or plant variety is typically unable to grow (Bohnert H. J and Jensen. R. G., 1996 TIBTECH 14:89–97). Many biochemical and physiological-basis for plant stress tolerance remain to be studied at the molecular level. However, it does appear that common damage from different stress (drought, salinity and cold stress) is mostly due to dehydration (Smirnoff N., 1998 Curre. Opi. Biotech. 9:214–219). The response that distinguishes drought (water stress)-tolerant and -sensitive plants more clearly is a dramatic accumulation of ions and solutes in tolerant species that leads to osmotic adjustments (Bohnert H. J and Jensen. R. G., 1996 TIBTECH 14:89–97). Drought and mineral nutrition may interact in a number of ways as a consequence of either (1) reduced transport of ions through the soil to the roots or (2) modified uptake of ions by roots. Potassium is particularly important in plants not only as a nutrient, but also as an osmoticum. Potassium may make a 30–50% contribution to water potential, particularly in older leaf tissue (Munns R. et al., 1979 Aust. J. Plant Physiol., 6:379–389). After prolonged drought in the field, potassium accumulates in leaves of ryegrass and barley, and could have a role in osmotic adjustment. In addition, potassium plays a key role in stomatal opening. A reduced supply of potassium therefore reduces stomatal conductance of CO2 much more than it reduces internal conductance (Terry, N. and Ulrich, A., 1973 Plant Physiol. 51:783–786), because potassium is lost from the guard cells (Ehret, D. L. and Boyer, J. S. 1979 J. Experi. Bot. 30:225–234).
The fact that plant roots can absorb potassium over more than a 1000-fold concentration range and the concentration dependence of potassium uptake by a root has complex kinetics suggests the presence of multiple potassium uptake systems. Gene families encoding inward-rectifying potassium channels have been identified in several plant species. The AKT1 potassium channel gene is predominantly expressed in roots and genetic analysis indicates that it mediates the uptake of potassium in both the micromolar and millimolar ranges (Hirsch, R. H., et al., 1998 Science 280:918–921). Active transporters also participate in potassium uptake and several candidate genes encoding energized transporters have been identified (Hirsch. R. E and Sussman. M. R, 1999 TIBTECH. 17:356–361). In the past decade, study of potassium channels in plants has been focused on their function at the molecular level, yet none of the genes has been shown to improve stress tolerance in planta.
Due to the commercial consequences of environmental damage to crops, there is an interest in understanding how to improve a plant's response to environmental damage. By improving a plant's performance or survival in response to cold, drought and salinity, the environment stress-related risks of farming can be reduced. This invention fulfills this need by providing an improved method for modifying the response of a plant to environmental stresses, and in particular, provides nucleic acid and amino acid sequences of a novel potassium channel involved in plant stress responses.